Ok, so we've all heard that there are many things that can affect the amount of breast milk your body produces. Some examples of things that may reduce the amount of milk you make are: caffeine, smoking, dehydration, diet low in nutrients...and I'm sure there are more.
Here's my experiences...
First, I'm a smoker, though I have cut down considerably. I have not noticed smoking affecting my milk. Nor have I noticed any difference, no matter how much coffee I drink, and I can go through 4-5 cups a day, depending on whats going on.
What I have found to decrease my milk supply is soda, caffeinated or not (I don't drink diet), lack of sleep, and lack of protein in my diet.
If I drink soda, it's almost certain that the next time little Archer wants to eat, he's gonna have to take a little less that he would like, but he makes up for it by nursing again sooner than he normally would. As long as I don't gulp soda all day, my milk goes back to normal. If I don't get enough sleep, I hardly make any milk at all, and a lack of protein not only decrease milk production, but also makes me more tired.
These are just my experiences, I know everyone's body is different.
Things I have noticed that seem to boost milk production are: cashews (recommended by my wonderful midwife), drinking milk or water, eating fresh fruits or lightly cooked veggies (I'm not big on raw veggies, but to each his own) and if all else fails, I take a multi-vitamin (I take the NOW brand VIT-MIN 100, which is a "high potency multiple, sustained release, includes trace minerals" and its has 25 mg psyllium husks fiber which about the same as a serving of metamucil disolvable powder).
These are just my experiences. If you have questions about breast feeding, talk to your doctor, midwife, lactation specialist, or contact your local Le Leche League leader.
Happy Nursing! :)